The influence of moisture on the permeability of crushed shale samples

Shale cuttings and cores recovered from the subsurface and stored for hours to decades tend to dry out and lose moisture and hydrocarbons, leading to an increase in the effective matrix permeability. Moisture loss in shale samples is a fundamental sample preservation problem which can be solved by applying a standard moisture equilibration procedure to restore lost moisture. Our aim was to investigate the relationship between permeability and variable moisture as-received, as-received moisture-equilibrated and saturated moisture-equilibrated samples. Samples were crushed to a series of particle sizes (0.6- 2.0) mm and moisture equilibrated at 97% relative humidity. Results show that moisture equilibration in the samples was achieved after 72 h. The permeability of the saturated moisture-equilibrated and as-received moisture-equilibrated samples decreased exponentially with increase in moisture content. The high correlation coefficient between permeability and particle size (r = 0.96 and 0.97) for moisture-equilibrated samples compared to 0.76 for as-received samples indicates that moisture equilibration improves permeability measurements in crushed shale samples. Furthermore, permeability measurements are repeatable for moisture-equilibrated samples compared to samples that were not equilibrated (as-received). We conclude that moisture content affects permeability and moisture equilibration normalizes and improves the repeatability of permeability measurements in crushed shale.